1. Field of the Invention
The present invention relates to a detecting apparatus and, more particularly, to an apparatus for detecting cell gap of a liquid crystal display panel speedily.
2. Description of Related Art
The conventional liquid crystal injecting method is achieved through follow steps: first aligning and pressing an upper substrate and a lower substrate to form a panel; placing the panel in a liquid crystal tank; and then vacuuming the cell and soaking the panel into a liquid crystal tank to inject liquid crystal into the panel through the effect of pressure difference and capillarity. But, the liquid crystal display panel is getting larger and thinner, the conventional liquid crystal injecting method takes long time and waste liquid crystal material, which increases the manufacturing cost. Another one-drop fill (ODF) method is achieved by dropping liquid crystal directly on a substrate, and then aligning and pressing an upper substrate and a lower substrate to form a liquid crystal display panel (LCD panel). This ODF method can save a lot of liquid crystal filling time and liquid crystal material, especially for super large size panel. However, in the ODF process, if the filling amount of liquid crystal is too much, user will observe gravity mura eventually in a period after processing.
As shown in FIG. 5, a cell gap of a liquid crystal display 91 is defined by spacers 930 between an upper substrate 910 and a lower substrate 920. Most of liquid crystal displays 91 are held vertically on a table 92, therefore, liquid crystal 93 is affected by gravity force 94 continuously. If the filling amount of the liquid crystal 93 is too much or the thickness of the cell gap is not uniform, the liquid crystal 93 will be continuously affected by gravity force to move downward and accumulate at the lower part of the display 91 that causes the failed display image which is called gravity mura. This gravity mura will reduce picture quality and life time of the display.
The gravity mura cannot be found in the early steps of the manufacturing process until a high temperature aging process proceeds. Generally, the gravity mura does not appear immediately due to low fluidity of the viscous liquid crystal and small difference of the non-uniform cell gap. Furthermore, during the high temperature aging process, the spacers, the substrates and the liquid crystal have different coefficient of expansion, therefore, volume of the liquid crystal will extend due to the heat from the high temperature aging process. When liquid crystal is too much, it will change the thickness of the cell gap, which causes the spacers cannot be used for fixing the thickness of the cell gap anymore, and forms an opening. Afterward, the liquid crystal at the upper part starts to accumulate downward to lower part of the liquid crystal display panel via the opening, which forms a liquid crystal display panel with gravity mura problem.
However, after filling the liquid crystal into the cell gap, there are still many complicated processes, such as aligning, pressing and cutting, that need to be performed before high temperature aging process. Moreover, to accumulate the liquid crystal in the lower part of the liquid crystal display panel during the high temperature aging process is taking long time to detect the non-uniform cell gap. Therefore, the entire detection process takes very long time and the panel yield cannot be controlled immediately.
Therefore, it is desirable to provide an apparatus for detecting abnormal gap between substrates of a liquid crystal display panel to mitigate and/or obviate the aforementioned problems.